1. Field of the Invention
The present invention relates to an endoscope including an insertion channel in an insertion portion.
2. Description of the Related Art
Conventionally, endoscopes have been widely used in a medical field, and the like. There is a desire for an endoscope having a distal end portion of a reduced diameter in order to alleviate pain of a patient at the time of examination. It is indispensable for a transnasal endoscope, in particular, which performs treatment and therapy by nasally inserting an insertion portion from the nose, to reduce the diameter size of a distal end portion.
Treatment and therapy are performed by inserting a treatment instrument such as a forceps into an insertion channel provided in the insertion portion of such an endoscope.
However, according to an endoscope in which a distal end rigid member as a main constituting member of a distal end portion is made of metal, when treatment and therapy are performed by inserting a high-frequency treatment instrument into an insertion channel, it would be likely that a leakage current caused by high-frequency output of the high-frequency treatment instrument flows in a body of a patient through a distal end rigid member.
Therefore, an endoscope including an insulating distal end cover configured to cover a metallic distal end rigid member is proposed in prior arts.
In addition, when an image pickup device is fixed to a metallic distal end portion (irrespective of presence or absence of the distal end cover), there is a possibility that a leakage current at the time of high-frequency treatment will flow in the image pickup device through a metallic portion of a distal end member. As a result, noise is likely to occur in an output signal of the image pickup device.
Therefore, an endoscope is proposed in which a size reduction of a distal end outer diameter is realized by configuring a distal end rigid member by resin and a leakage current caused by high-frequency output is prevented from easily flowing in an image pickup device.
For example, Japanese Patent Application Laid-Open Publication No. 2006-122498 discloses a configuration related to an endoscope which includes a distal end rigid member made of resin, a metallic connecting pipe fixed to the distal end rigid member, and a distal-most joint ring (also referred to as a bending piece) which is soldered to a rear end portion of the connecting pipe to be electrically connected to the connecting pipe, wherein a leakage current caused by high-frequency output of the high-frequency treatment instrument is allowed to flow to a ground member of an insertion portion, such as a joint ring of a bending portion, through the connecting pipe.
Furthermore, a conventional endoscope including a distal end rigid member made of metal and a distal end cover configured to cover the distal end rigid member has usually achieved a conduction between the distal end rigid member and a joint ring and prevented the joint ring from falling off to a forward side of the distal end rigid member by fixing the distal-most side joint ring to the distal end rigid member by mounting using a screw and the like.